This invention relates to typewriters and more particularly to a keylever touch control mechanism for selectably varying the force required to depress a keylever.
Desirable features of touch control mechanisms for typewriters are simplicity, economy, and adjustability. Meeting these requirements has resulted in a variety of mechanisms.
For example, one such touch control mechanism as shown in U.S. Pat. No. 2,098,285 to C. Gabrielson et al, teaches a plurality of keylever coil springs that couple a plurality of keylevers to a common bail. The spring tensions are individually adjustable for each keylever and collectively adjustable for all keylevers by pivoting the bail through a control means.
The many parts in such mechanisms resulted in a complex and costly design.
An improved design as shown in U.S. Pat. No. 3,229,798 to A. Grashoff, included a spring urged common bail underlying all keylevers and selectively biased against the keylevers in a plurality of positions by an adjustable detent. Still another improved design, as shown in U.S. Pat. No. 2,528,450 to J. L. Petz, that incorporated a rigid plate underlying a flat spring tension comb to support and restore the keylevers was introduced.
None of the prior art provides for a simple and inexpensive variable keylever spring force to be exerted between the different rows of keylevers to offset the different lengths of keylevers in the different rows. Furthermore, none of the prior art provides for the engagement of an additional spring system to provide maximum force to depress a keylever and the disengagement of the additional spring system to necessitate minimum force to depress a keylever.